Pressure sensing device for pipes
BACKGROUND OF THE INVENTION 
     The present invention relates to a pressure sensing device for use in pipelines transporting slurries, corrosive or abrasive fluids wherein it is essential to isolate the pressure gauge from the fluid being transported. A thin metal wall forming a portion of a removable sleeve serves as a means to transmit pressure signals from the fluid medium being transported within the pipeline to a liquid filled pressure sensing chamber operatively connected to a pressure gauge. The thin metal wall is provided with means to permit the wall to move inwardly and outwardly in response to small pressure changes. 
     There are numerous pressure gauges in the prior art which are particularly adapted to isolate the pressure media from the sensor. These devices provide for a diaphragm or membrane which forms a barrier between the media passing through the pipeline and a fluid filled chamber on the opposite side of the diaphragm with the fluid filled chamber being operatively connected to a pressure gauge. Thus, the diaphragm or membrane responds to pressure fluctuations within the fluid passing through the pipeline and transmits pressure signals to the fluid within the isolating chamber which in turn actuates the pressure gauge. Examples of such devices are the Classen U.S. Pat. No. 4,425,800, Borsanyi U.S. Pat. No. 3,863,504, Knecht U.S. Pat. No. 4,773,269 and Mayhew U.S. Pat. No. 4,840,068. 
     The Classen U.S. Pat. No. 4,425,800 discloses a device for determining the internal pressure in a fuel injection pipe system wherein a housing member has a wall portion of reduced thickness so as to act as a membrane and which transmits the pressure signals from the pipe system to a sensor device. The Borsanyi U.S. Pat. No. 3,863,504 discloses a pressure gauge wherein the instrument is separated from the pipeline by a flexible diaphragm. The Knecht U.S. Pat. No. 4,773,269 also provides a deflecting diaphragm member which senses a pressure within a chamber and by deflection of the diaphragm a change of resistance takes place in a strain gauge mounted on the diaphragm. The Mayhew U.S. Pat. No. 4,840,068 provides a pipe pressure sensor in which an elastomeric member is utilized as a flexible diaphragm disposed between a pipeline and a pressure sensing liquid chamber. 
     There are, however, problems in connection with the use of such prior art devices. Flexible elastomer diaphragms tend to absorb liquids and are damaged by corrosive media and slurry particles passing through the pipeline. Accordingly, the response of such diaphragms vary considerably depending upon the condition of the elastomer. Pressure sensors which utilize relatively thin metal walls as a means for separating the pipeline media from contact with the pressure gauge do not respond well to small pressure changes due to a lack of flexibility and, of course, such elements are subject to deterioration by corrosion and the like. Furthermore, not one of the prior art devices provides means for measuring pipe pressure around the entire circumference of the fluid stream. It can be appreciated that in large pipelines carrying heavy slurries the weight of the slurry itself will have an appreciable effect on pressure measurements and hence it is essential to provide a means for measuring the pressures around the entire fluid stream. 
     According to the present invention, there is provided a pressure sensing device which includes a readily replaceable sleeve having a thin walled metal member which serves as a pressure sensing diaphragm extending around the entire circumference of the fluid stream. The metal pressure sensing diaphragm is provided with means comprising pressed out accordion-like pleats or folds to permit movement of the diaphragm in response to small pressure changes so as to provide a highly accurate pipe pressure measuring device. Thus, the present invention overcomes the above-noted disadvantages of prior art pipeline pressure gauges by utilizing a thin walled metal diaphragm having accordion-like folds therein extending 360° around the periphery of a fluid stream to permit instantaneous response to small variations in pressure within the pipeline. The sensing diaphragm is mounted on a sleeve which is screw-fit within the body member with the pressure gauge mounted externally of the body member. Thus, the sleeve may be readily replaced in the event the diaphragm becomes damaged. 
     An object of the present invention is to provide a pipeline pressure sensor which utilizes a metallic diaphragm including accordion-like folds to ensure accuracy of pressure measurements. 
     Another object of the present invention is to provide a pressure sensing device for pipelines in which the pressure sensing diaphragm extends around the entire periphery of the fluid stream. 
     Other objects and many of the intended advantages will become more readily apparent upon consideration of the following detailed specification when considered in connection with the accompanying drawings wherein: 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view partly in section of a pressure sensing device according to the present invention mounted in a pipeline, and 
     FIG. 2 is a cross section view of the pressure sensing device along the line 2--2 of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more specifically to the drawings there is shown at 1 in FIG. 1 a pressure sensing device which is adapted to be inserted in a pipeline to sense the pressures of fluid passing through the pipeline. The pipeline is shown at 2 and the pipeline has flanges 3 extending around the entire periphery of the pipeline with apertures in the flanges to receive bolts 4. As seen in FIG. 2 the pressure sensing device 1 is fit between flanges 3 on pipeline 2 and is retained in position within the pipeline by bolts 4. When it is necessary to service the pressure sensor 1, it is merely necessary to unscrew the bolts 4 and remove the pressure sensor. 
     The pressure sensor according to the present invention comprises essentially three parts, a body member 5, a sleeve member 6 which is screw-fit within the body member 5 and a pressure gauge 7 which is screw-fit in an external bore in the body member 5. 
     The body member 5 comprises a ring shaped member having screw threads 8 at the end portions of the internal surface. The central portion of the internal surface of the body member has a circumferential recess 9 which is provided with a passageway 10 having a screw-threaded end portion 11 to receive the sensing port of pressure gauge 7. A fluid filling port 12 is also provided in the body member 5. 
     The sleeve member 6 has a recessed central portion 13 which extends around the entire external surface of the sleeve. The end portions of the sleeve 6 are screw-threaded to mesh with the screw-threaded end portions 8 of the body member 5. It can be seen in FIG. 1 that when the sleeve member 6 is fitted within the body member 5 the recess 9 in the body member aligns with the recessed portion 13 of the sleeve to form a chamber which extends around the entire periphery of the sleeve member and body member. The central portion of the sleeve member 6 comprises a thin wall which has a plurality of pressed out pleats or folds as shown at 15. As seen in FIG. 1 the pressed out portions are elliptically shaped and in the embodiment shown there are four such pressed out portions equidistantly spaced around the periphery of the internal surface of the sleeve 6. 
     In use a sleeve member 6 is screw-fit into the body member 5 so that the recess 9 in the body member and recess 13 in the sleeve member are aligned to form a sensing chamber. The sensing chamber and passageway 10 are filled through the filling port 12 and the filling port is subsequently plugged. The pressure sensing device is then inserted in a pipeline as shown in FIG. 1. Fluid passing through the pipeline will cause the thin walled central portion 14 of the sleeve 6 to move outwardly in response to pressures within the pipeline. It can be seen that the pressure sensing diaphragm 14 will respond to pressures around the entire periphery of the fluid stream passing through the pipeline. The pressed out portion 15 forming accordion-like folds or pleats within the diaphragm will permit the diaphragm to respond to both small pressure variations as well as large pressure fluctuations at any point around the pipeline. 
     It can be seen that the pressure sensing chamber formed by the recesses in the body member and sleeve member provides an isolating chamber to prevent any materials within the pipeline coming in contact with the pressure gauge 7. In the event that the pressure diaphragm formed by the central portion of the sleeve member 6 becomes damaged by corrosive materials or the like within the pipeline, the sleeve member 6 may be easily removed and replaced. 
     Obviously many modifications and variations of the present invention are possible in light of the above teachings.